1. Field of the Invention
The present invention relates to a mobile device, and more particularly, to a mobile device and a method capable of minimizing the discharges of a backup power supply which provides backup electric power to the mobile device when a main battery is detached from the mobile device.
2. Description of the Related Art
In general, mobile devices such as PDAs, cellular phones, and so on, operate with a battery that can be loaded and unloaded in and out of the mobile devices, and have a backup battery to preserve data stored in a memory device built into the mobile devices when the battery is detached from the mobile device due to external impacts. The backup battery is generally charged with a voltage supplied by the battery, and the output current rate of the backup battery does not exceed several tenths of a mA, and the backup battery runs out in merely a few hours.
FIG. 1 is a block diagram illustrating an operation of a backup battery for a conventional PDA.
In FIG. 1, the conventional Personal Digital Assistant (PDA) includes a Code Division Multiple Access (CDMA) module 10, a control unit 20, a Dynamic Random Access Memory (DRAM) 30, and a backup battery 40. The PDA further includes a display unit, an I/O interface unit, and so on, however these components are omitted since they are not necessary to explain the operation of the backup battery.
The CDMA module 10 is built into the PDA, but may be loaded into and unloaded out of the PDA depending upon the type of PDA. Although FIG. 1 shows an implementation of a CDMA module 10 with a communication function, other types of function modules, such as a wireless LAN card or a television tuner may also be adequately used.
The control unit 20 includes application programs and an operating system, and runs the application programs or controls the CDMA module 10. That is, when the CDMA module 10 is not used, the control unit 20 can turn the CDMA module 10 off with an application of a control signal P_OFF to the CDMA module 10. However, it takes a considerable amount of time to notify a base station (not shown) of the cutoff of electric power to the CDMA module 10 and to turn the CDMA module 10 off.
The DRAM 30 stores temporary data during application program executions by the control unit 20 and data resulting from the application program executions by the control unit 20. The DRAM 30 is low in cost compared to SRAM or Flash ROM, therefore the DRAM is widely used in mobile devices such as PDAs. However, the DRAM has a disadvantage of losing all its data stored therein when the electric power is cutoff.
In the conventional PDA mentioned above, when the main battery is detached from the PDA due to external impacts during data communications between the control unit 20 and the CDMA module 10, the backup battery 40 supplies power to the DRAM 30 and the control unit 20. When the CDMA module 10 and the control unit 20 have been in data communications and communication data has been in a logic “high”, the backup battery 40 runs out due to a load RL of the CDMA module 10.
When the main battery (not shown) which supplies power to the CDMA module 10 and the control unit 20 is detached from the PDA, current consumption occurs during a period of time ranging from a few milliseconds to a few tenths of a millisecond in data lines and control signal lines data/control which are wired between the control unit 20 and the CDMA module 10.
When the control unit 20 communicates data with a function module such as the CDMA module 10 consuming large currents and communication data is mainly formed in a logic “high”, more current is consumed. Accordingly, there exists a problem in that the backup battery 40 with a current rate of a few tenths of a mA in general, can preserve the data stored in the DRAM 30 for less time, depending upon the amount of discharge currents by the CDMA module 10.